Various systems project or display information that a user is expected to interact with, at least indirectly. For example, computers often display a document on a monitor, and the user is expected to interact indirectly with the displayed document by using a mouse to position the cursor within the displayed document. Such computers may also project the document onto a projection screen using a projector, rather than displaying the document on a monitor. As another example, touch screen computers allow a user to interact more directly with a displayed image by touching the monitor at positions indicated by the image itself, such as, for example, touching a particular element in a displayed image in order to select that element.